I guess some might call it ambiance, while others will call it frequencies over 14,000 hz, which many people can't hear that well anyway unless they are at a very high volume. All this talk that human hearing is 20-20,000hz is deceptive.

However, contrary to popular belief, the author is not aware of any scientiﬁc experiment which showed beyond doubt that there is any listener (trained or not) able to detect the difference between a (complex) musical signal with content up to 20 kHz and the same signal, but bandlimited to around 16 kHz. To make it clear, there are some hints to the fact that there are listeners with such capabilities, but the full scientiﬁc proof has not yet been given. As a corollary to this (for a lot of people unexpected) theorem, it is a good encoding strategy to limit the frequency response of an MP3 or AAC encoder to 16 kHz (or below if necessary).

Usually if you can't quite figure out whats wrong with an encoded file, its because theres nothing wrong and you're getting fooled by placebo. Every single time I've passed a blind test I've been able to say exactly what was wrong. Usually when I thought something was off but wasn't sure, I ended up failing the test.

There's quality and then there's capability. The perceived sound quality can be affected (in part) by poor impedance matching, sensitivity of ear device and output current. The trick is to get a good match between player and ear device.

There's quality and then there's capability. The perceived sound quality can be affected (in part) by poor impedance matching, sensitivity of ear device and output current. The trick is to get a good match between player and ear device.

I get what you're saying, but its worth remembering that headphones are not (and should not) be impedance matched. You want much lower impedance on the device then the headphones, which is why low impedance headphones tend to be harder to drive.